Anomalous Behavior of Ultra-Low-Amplitude Capillary Waves. A Glimpse of the Viscoelastic Properties of Interfacial Water?

Abstract

We investigate, both theoretically and by a differential interferometric technique, the behavior of large-wavelength capillary waves (of the order of 10 m) selectively excited at the surface of drops and bubbles with typical eigenfrequencies of the order of 10 Hz. The resonance peaks of gas bubbles or hydrocarbon drops in water (radius less than 1 mm) highlight anomalously small dissipation in the region of ultralow (sub-nanometric) oscillation amplitudes, reaching a plateau at higher amplitudes. This is in sharp contrast to the usual oscillating systems, where an anomalous behavior holds at large amplitudes alone. Dissipation is strongly dependent on the excited vibrational modes and, in spite of remarkable numerical differences, water-vapor and water-hydrocarbon interfaces exhibit the same overall trend. A phenomenological model was developed, based on the assumption that water possesses a threshold viscoelasticity, above which it behaves like a regular viscous fluid. The well-known Deborah number was then estimated within the anomalous region and found to lie in the range of viscoelastic fluids. In agreement with previous studies of nanohydrodynamics (e.g., atomic force microscopy measurements with sub-nanometric tip motions), the present one lends support to the idea that every self-aggregating fluid exhibits yield stress behavior, including classical Newtonian fluids like water. The essential requirement is that the applied perturbation lie below a critical threshold, above which viscous behavior is recovered. Our differential interferometric technique seems particularly suitable for this type of studies, as it allows measurement of long-wavelength capillary waves with sub-nanometric resolution on the oscillation amplitudes.

Interferometric detection of hydrodynamic bubble–bubble interactions

“…The proposed method is based on the extension of an interferometric technique developed in the framework of studies of single oscillating gas bubbles and drops (Corti, Bonomo & Raudino 2012; Corti, Pannuzzo & Raudino 2014, 2015; Cantu’, Raudino & Corti 2017; Raudino, Raciti & Corti 2017; Corti et al. 2018).…”

“…The differential nature of the interferometer allows a sensitivity of 0.1 nm in the oscillation amplitude measurements (Raudino et al. 2017). The optical components are carefully arranged so to avoid beam crossing or spurious reflections.…”

“…The proposed method is based on the extension of an interferometric technique developed in the framework of studies of single oscillating gas bubbles and drops (Corti, Bonomo & Raudino 2012;Corti, Pannuzzo & Raudino 2014Cantu', Raudino & Corti 2017;Raudino, Raciti & Corti 2017;Corti et al 2018). While the detection principle remains unaltered, the main novelty is the independent detection of the two bubbles, set at finely regulated mutual distances, whose interactions are evaluated from the variations in the resonance features along the distance.…”

Anomalous sorption kinetics of self-interacting particles by a spherical trap

“…Motivated by these findings, we have recently undertaken a combined study by using theoretical, experimental and Molecular Dynamics approaches [20][21][22][23][24][25][26][27]. Aim of this long-term project is to build-up a precise and tunable biomimetic system described by forced oscillating drops or bubbles, eventually dressed by a surfactant coat mimicking the cell membrane.…”

Protein Adsorption at the Air–Water Interface by a Charge Sensing Interferometric Technique

“…A much deeper insight up to the nanometric scale can be achieved by employing techniques such as the interferometric ones grounded on the undulatory nature of the light. The differential interferometric techniques applied here deeply extend the range of investigable amplitudes from tens of nanometers to the subnanometer range. , The bubble interferometer exploits the analysis of stationary modes of a resonating bubble under small perturbations induced by an external electromagnetic (e.m.) force field and allows the study of surface properties with extremely high sensitivity. Importantly, the technique is complementary to the drop/bubble profile methods because it is sensitive to the charge at the interface .…”